Many different techniques and combinations of materials have been used for making small diameter nozzles for ink jet printers. Punching, laser drilling, molding, and machining have been reported as methods for making ink jet nozzles. One of the most useful and economical methods for making small holes, especially where hundreds of jets in an array are required, is by electroforming around or over small dielectric cylinders, or posts, formed of photo-imaged resist polymer. This geometry is described in numerous patents related to methods for making orifice plates, such as Kenworthy U.S. Pat. No. 4,184,925; Cloutier U.S. Pat. No. 4,528,577; and Sexton U.S. Pat. No. 4,971,665.
A need exists for smooth over plated nozzles at very close spacing for high density arrays (i.e., greater than 300 jets/inch). The problem is that the electroplating grows in thickness at nearly the same rate that the electroplating grows laterally over the dielectric post. If the posts are necessarily very small in diameter because of the close spacing, the resultant thickness of nickel is very small. For example, at jet density of 600 dpi and an orifice diameter of 0.0006 inch, the plating thickness is practically limited to 0.0005 inch thickness when plating over 0.0016 inch diameter posts. Foils at this thickness are fragile and subject to distortion during handling and use.
The present invention meets this need and provides a high density array by this method.